The general trend for water temperature in aqueous cleaning applications is that hotter is better. Running hotter water in equipment is also generally more expensive. To allow a good process window, we design most of our water soluble fluxes to be cleaned in room temperature de-ionized water. With this in mind, you have some “wiggle-room” in your process to turn up the heat if you want to run a longer or hotter than normal reflow (which may char a flux, impacting cleanability).